The present disclosure relates generally to electromagnetic actuators and, more specifically, to a variable force solenoid having a permanent magnet.
Electromagnetic actuators (e.g., a variable force solenoid) typically include a wire coil positioned within a housing and around a moveable armature. A current can be applied to the wire coil to produce a magnetic field which can then actuate (i.e., move) the moveable armature with respect to the housing. Current trends are leading towards improving the output force and efficiency of electromagnetic actuators; however, this requires decreasing magnetic losses by, for example, reducing air gaps within the electromagnetic actuators. This reduction in the air gaps within an electromagnetic actuator can result in increasingly higher starting flux (e.g. pin fully retracted into solenoid housing), as the reluctance of the magnetic circuit can be lower under all operating conditions. The higher starting flux, as a result of the reduction in the air gaps, can require the parts (e.g., housing, armatures, etc.) that carry the flux to require more area (e.g., increased thickness, larger diameters, etc.) to prevent magnetic saturation. Increasing the area of the flux carrying components can lead to added cost due to additional material, and also require more space, which offsets a desirable outcome of making the electromagnetic actuator smaller.
Additionally, a reduction in air gaps can extremely tighten the tolerances and clearances, which, for manufacturing purposes, can prohibitively increase costs. Furthermore, a reduction in the air gaps can lead to high side loading forces (i.e., forces substantially perpendicular to the desired direction of actuation) if the armature is not kept fully centered.